Rotary kinetic fluid motors or pumps – With passage in blade – vane – shaft or rotary distributor...
Reexamination Certificate
1999-05-17
2001-07-31
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With passage in blade, vane, shaft or rotary distributor...
C416S09700R
Reexamination Certificate
active
06267552
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an arrangement of holes for forming a cooling film on a component wall subjected to a flow of hot gas, the component being in particular a turbine vane or blade or a combustion chamber of a gas turbine,
2. Discussion of Background
The publication “Journal of Engineering for Power”, April 1978, Vol. 100, Pages 303 to 307, reveals a test set-up for the simulation of a cooling film, in which a flat plate is provided with holes which represent the ejection openings of tubes set at an angle of 35° relative to the plane of the plate. The holes are arranged in the form of two rows which are staggered and laterally offset relative to the main flow direction.
The series of tests described in this article indicate a marked increase in the cooling effect relative to an individual row of holes. This effect is attributed to the fact that the jets of cooling air emerging from the first row deflect the cooling air jets emerging from the second row onto the surface of the wall to be cooled and, by this means, increase their cooling effectiveness. In addition, the cooling film of the first row of holes forming further downstream is located above the cooling film of the row of second holes and additionally protects the latter from the penetration of hot gas.
DE 35 08 976 A1 shows a turbine vane or blade which, because of the high level of thermal loading, is provided with a plurality of rows of holes in order to form cooling films. In the stagnation point region and adjacent to it on the suction surface, three adjacently located rows of holes are provided in each case in order to further increase the cooling effect in these particularly highly thermally loaded wall portions of the turbine vane or blade. In this arrangement, it is accepted that the cooling air requirement is increased because of the many rows of holes.
A similar direction is indicated by the turbine vane or blade known from EP 0 501 813 B1 in which various variants of hole arrangements in a double row are proposed for the formation of a cooling film. One of the variants proposes allocating two holes of small diameter in the first row to each hole of larger diameter in the second row. The association of the holes in the first row with the respective holes in the second row follows from the fact that these are configured as flow branches of a common inlet opening.
Disadvantageous in this solution is again the high consumption of cooling air, which is caused by the large number of outlet openings in the first row. A further disadvantage may be considered as being the low flexibility in the selection of the direction of the individual holes because the latter start from a single, common inlet hole. In particular, the cooling air jets emerging from the holes in the first row have directional components extending in different directions which point laterally, i.e. at right angles to the main flow, which is undesirable in many cases.
SUMMARY OF THE INVENTION
The invention attempts to avoid the disadvantages described. Accordingly, one object of the invention is to provide a novel arrangement of holes, of the type described at the beginning, which makes it possible to form a cooling film of high efficiency with a reduced cooling air requirement.
In accordance with the invention, this is achieved in an arrangement of holes, by the number of holes in the first row being substantially equal to or smaller than the number of holes in the second row.
In contrast to the previously usual tendency to improve the effectiveness of the cooling film by providing a further row of holes or by increasing the number of outlet openings in the first row, the opposite path is followed in the present case. It has, surprisingly, been found that the effectiveness of the cooling performance can be increased if a hole of smaller diameter in the first row is associated with each hole of the second row. This therefore results in substantially equal numbers of holes in the first and second rows.
With respect to the effectiveness of the cooling performance, it has been found particularly effective for the outlet openings of the holes in the second row to be arranged, relative to the direction of the flow of hot gas, offset to the side of the outlet openings of the holes in the first row. It is considered optimum that the outlet openings of the holes in the second row should be provided downstream in the center between the outlet openings of the holes in the first row.
Particularly effective superpositioning of the partial film formed by the holes in the first row on that of the second row results when, in accordance with a preferred variant, the holes in the first row are aligned with their axes substantially parallel to the holes in the second row.
Tests have shown that the cooling effect is an optimum when the diameter of the hole of the first row is greater than or equal to half the diameter of the holes in the second row. The last-mentioned condition, in particular, offers an optimum compromise between an outstanding effectiveness of the cooling performance, on the one hand, and a minimal requirement for cooling air, on the other.
In this connection, the selection of the distance between the two rows is also of particular importance. Values for the distance have been found to be optimum which are smaller than or equal to five times the arithmetic average of the diameter of the holes of the first and second rows, i.e. which satisfy the following equation:
p≦5(d
1
+d
2
)/2,
where
p is the distance between the two rows,
d
1
is the diameter of the holes in the first row and
d
2
is the diameter of the holes in the second row.
A further improvement in the cooling effectiveness can then be achieved if the holes in the second row, at least, have an axial portion with a funnel-shaped variation of cross-section in the region of the outlet openings. The increase in the cross section in the outlet plane achieved by this leads to a reduction in the outlet velocity of the partial cooling flows. It can then be advantageous for the axis of rotation of the funnel-shaped axial portion not to extend coaxially with respect to the axis of rotation of the rest of the hole but to be inclined somewhat in the direction of the main flow. This brings the emerging cooling air jet substantially closer to the surface to be cooled.
Although the reason for the positive properties of outlet openings which widen in the shape of a funnel are known, this feature is much more expensive than cylindrical bores. The reason is that the outlet openings have to be shaped with a high level of precision because, otherwise, the emerging cooling air flows do not form a well attached cooling film. This demands an expensive manufacturing process (EDM process).
This problem does not arise in the case of the arrangement of holes in accordance with the invention. In this arrangement, funnel-shaped outlet openings formed by means of laser have the same cooling efficiency as those outlet openings which have been manufactured with high precision with the previously employed spark erosion process because the jet from the first cooling hole presses the cooling air jet from the funnel-shaped hole onto the wall. This makes it possible to employ the relatively low-cost laser method for forming funnel-shaped outlet openings.
A further increase in the cooling performance can be achieved if, in an especially preferred variant, the holes in the first row also have an axial portion with funnel-shaped variation of cross-section in the region of the outlet openings. In this case, it is additionally necessary to meet the condition that the area of each of the outlet openings in the first row is smaller than the area of each of the outlet openings in the second row.
REFERENCES:
patent: 4676719 (1987-06-01), Auxier et al.
patent: 4726735 (1988-02-01), Field et al.
patent: 5096379 (1992-03-01), Stroud et al.
patent: 5374162 (1994-12-01), Green
patent: 5577889 (1996-11-01), Terazaki et al.
patent: 5586859 (1996-12-01), Nolcheff
patent: 58167
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Look Edward K.
Woo Richard
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